Adding char from char array to char arraylist

Question

I'm trying to add a char to an ArrayList of Chars from an array of chars for reasons I won't talk about for fear of making the post long. I am using this basic code:

for(char ch: c){
    this.age.add(ch);
}

Where c is the array, and age is the ArrayList. Keep in mind that age is not initialized, therefore it is null. My question is, why am I getting a null pointer exception when I compile and run this?

The answer is in the question. age is not initialized, therefore it's null, therefore trying to call a method on it will throw a NullPointerException. Corollary: to avoid the exception, age needs to be initialized before calling any method on it. — JB Nizet
– JB Nizet, Commented Nov 28, 2013 at 7:37
You don't need to initialize any element inside the list. You just need to create the list, which is empty by default: age = new ArrayList<>(); — JB Nizet
– JB Nizet, Commented Nov 28, 2013 at 7:39

Tom Jonckheere · Accepted Answer · 2013-11-28 07:56:08Z

3

You are getting a nullpointer because age, the Arraylist is null. You need to initialize it before you add elements.

List<Character>  age = new ArrayList<Character>();
for(char ch: c){
    this.age.add(ch);
}

Initialize age before the for loop, if you do it in the for loop you will reinitialize it each time and lose your data.

edited Nov 28, 2013 at 7:56

answered Nov 28, 2013 at 7:39

Tom Jonckheere

1,6483 gold badges21 silver badges39 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Suresh Atta · Accepted Answer · 2013-11-28 07:37:47Z

2

That might be you are not initialized age. initialize it like,

List<Character>  age = new ArrayList<Character>();

Exception coming because you just left it like

 List<Character>  age;

So by default reference is null. and calling a method on it's like

null.method()  //NullPointerException

answered Nov 28, 2013 at 7:37

Suresh Atta

122k38 gold badges206 silver badges315 bronze badges

2 Comments

comscis Over a year ago

ah I see. It's not initialized w/o the ending. Thanks!

Suresh Atta Over a year ago

@comscis Happens. Glad to help.

Collectives™ on Stack Overflow

Adding char from char array to char arraylist

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related